The present invention relates to a load carrying strut capable of withstanding loads in excess of its yield strength and is particularly concerned with such a strut which may be incorporated into a structure to absorb the energy of extreme cyclical loads, without destruction of the strut or structure. The invention is especially concerned with a strut capable of withstanding, without destruction, the extreme cyclical loads which occur in buildings and other structures during earthquake.
The prior art teaches the use of energy absorbers in structures subject to cyclic earthquake forces. Examples of such absorbers may be found in U.S. Pat. Nos. 3,833,093 and 4,117,637. Both of these patents suggest the use of a plastically deformed material, such as lead, to absorb the cyclic energy imparted to a structure during earthquake conditions. The absorbers of these patents, however, are not in the form of simple and inexpensive struts adapted for incorporation as load bearing members in the manner of the strut of the present invention.
An example of a prior art compression strut having telescoping elements somewhat like those employed in the strut of the present invention may be found in U.S. Pat. No. 4,052,029. In the strut of this patent, however, the compressible medium is crushed and is not suited for cyclic energy absorption thereafter.
Other efforts relating to energy absorbing shock absorbers may be found in the automotive art relating to vehicle structures capable of withstanding crash impacts. These structures, however, generally employ either springs which bounce back, or crushable elements which are not designed for cyclic loading or the maintenance of load carrying capacity after crushing.